In a pilot study of caffeine for daytime sleepiness in PD, there was evident benefit on the motor manifestations of disease. There have been other lines of evidence that have suggested caffeine could be useful in PD. This study is to evaluate the efficacy of caffeine 200 mg BID vs matching placebo for motor and non-motor aspects of disease. This will be in three stages. In the first six-month stage, medications will be held constant, to see whether caffeine does have motor benefits. Then we will perform a four-year extension stage to define if the effects of caffeine persist (or even magnify), and to see if caffeine helps reduce dose of other PD meds and/or prevents their side effects. Finally, we will finish with a six-month stage in which we will place all patients on caffeine - this will allow us to assess caffeine's use in later disease, but more importantly, will assess whether early use of caffeine produces long term changes beyond its immediate effects.